# Help with load cells

Hi!

I require your help regarding a problem I’m encountering.

I am trying to measure a cord speed using a load cell beam type,
I have tried many local load cells, at very low speeds they work fine,
But if i increased the speed the results start to fluctuate a lot,
now i am thinking of the Robotshop 100g Micro Load Cell,
Can somebody advice me what to do, or explain to me what is the problem and does the natural frequency of the load cell has anything to do with this

Thank you so much in advance for your help!

Hi,

We don’t see how you can measure a cord speed with a load cell. Could you provide more details ? Do you have a diagram that can better explain your idea ?

Sorry i made a mistake, I meant the tension of the cord

Thank you for you replay Mr. bdaouas

it will be something like this but its not an S shape load cell it’s beam type.

If the cord is moving there will be vibration in it that will likely show up in the load cell readings. That will probably worst at some particular speed because of the resonant frequency of the entire system. You may find some low-pass filtering to be useful.

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Exactly, as oldguy said, a low-pass filter would help a lot for vibrations.
In addition, when the cable moves at relatively high speeds, not only the load cell’s natural frequency would be important but also the load cell’s amplifier frequency response and your ADC’s sampling rate. You would need to calculate your highest frequency measurements at the cable’s highest speed and verify if your amplifier+ADC sampling rate is at least twice as that (Nyquist Theorem)

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Thank you very much Mr oldguy and Mr bdaouas for your information and advises,

But i think the problem that I’m facing only concern the load cell because i have another load cell working very very good without any fluctuating in the results and i am connecting them both to the same amplifier.

But i can’t get another load cell from the same type
for that reason i am trying many load cell and trying to find why that load cell working very good at high speeds while the other load cells don’t.

what do you recommend me to do ?

A load cell senses what is applied, unless it defective or pushed beyond its capabilities. Since the new load cell oscillations happen as the cord velocity increases, I doubt it is defective. However, the vibration frequency may be too fast for the “old” load cell to respond to, thereby creating a mechanical low pass filter.